1. Field of the Invention
This invention relates to optical devices.
2. Description of the Related Art
In opto-electronic signal transmission devices the delay of a radio frequency (r.f.) modulated optical signal is often required and is generally effected by the use of an appropriate length of optical waveguide, e.g., optical fibre. Such a delay device exhibits low loss, low dispersion and good thermal stability, but since the velocity of light in a typical optical waveguide is high, e.g. two thirds of the velocity of light in free space, long lengths of waveguide are typically required. This makes such a delay device difficult to incorporate in an integrated optical device, i.e. an optical device formed on the surface of a semiconductor chip.